Candela
Candela is the unit of luminous intensity and is the basic unit of the Si system. Candela is derived from the luminous intensity of a candle of a precisely defined composition. One candela is defined as the luminous intensity of a source that emits monochromatic radiation at a frequency of 540 × 10^12 hertz with a luminance of 1/683 watts per steradian in a certain direction.